Field of the Invention
The present application relates to an optoelectronic device, and more particularly to an image sensing device and a method for fabricating the same.
Description of the Related Art
In recent years, electronic consumer products such as digital cameras, digital video recorders, and mobile phones having image sensing devices capable of capturing images have become more and more popular. Accordingly, the demand for image sensing devices has increased. An image sensing device can receive a light signal and convert the light signal into an electronic signal. After processing the electronic signal, a digital image can be generated. In general, image sensing devices can be categorized into two types: charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) devices.
FIG. 1A is a sectional view of a conventional CMOS-type image sensing device 10. The image sensing device 10 typically comprises a silicon substrate 100 having a pixel array therein. Each pixel of the pixel array includes a photoelectric conversion unit 102, such as a photodiode, generating an electronic signal corresponding to the intensity of light. Here, only four pixels 100a, 100b, 100c, and 100d of the pixel array are shown in FIG. 1 for illustration. When light is focused on the photoelectric conversion units 102 of the pixel array, electronic signals can be generated to display a corresponding digital image. A microlens array 106 is disposed above the pixel array for focusing light on the photoelectric conversion units 102. Furthermore, a color filter array 104 is disposed between the pixel array and the microlens array 106, allowing the pixels 100a-100d to collect light with specific wavelengths.
FIG. 1B is a sectional view of a conventional image sensing system which comprises the image sensing device 10 as shown in FIG. 1A and a module lens 20 disposed above the image sensing device 10. When light passes through the module lens 20, it may spread out in a wide range, as indicated by the arrows in FIG. 1B. Thus, the incident angle of the light (i.e. chief ray angle (CRA)) at the periphery of the microlens array 106 is usually larger than that at the center of the microlens array 106. As a result, the focal length at the periphery of the microlens array 106 is shallower than that at the center of the microlens array 106, such that the intensity of the light to each photoelectric conversion unit 102 is reduced. The reduction of light intensity not only enhances cross-talk between the pixels 100a-100d but also reduces the signal-to-noise ratio (SNR) and photosensitivity of the image sensing device 10. Therefore, to develop a novel image sensing device with high quantum efficiency of the pixels and low cross-talk between the pixels has become a critical issue.